(i) Field of the Invention
This invention relates to a heat-exchanger in the form of a novel device for providing high efficiency of heat transfer from thermochemical heat sources to a flow of air, which device is especially useful for inhalation warming of hypothermia victims.
Hypothermia is one of the most frequently encountered and yet often overlooked aspects of emergency medicine. Hypothermia, like other medical conditions, is graduated by the degree of severity and the symptoms and urgency of treatment may differ radically at different levels. In mild hypothermia above 35.degree. C. (95.degree. F.), the accepted treatment is passive rewarming by natural or endogenous heat generation, which is simple, requires no equipment (other than a warm environment and/or blanket), and has no inherent morbidity. Moderate hypothermia occurs in the range of 32.degree. to 35.degree. C. (89.6.degree. to 95.degree. F.) and may produce loss of motor control, slurred speech and amnesia; marked hypothermia occurs at body core temperatures from 28.degree. to 32.degree. C. (82.4.degree. to 89.6.degree. F.) and is indicated by muscle rigidity, peripheral cyanosis and shock; and severe hypothermia occurs at temperatures from 25.degree. to 28.degree. C. (77.degree. to 82.4.degree. F.) at which the victim may have lost deep tendon reflexes and ventricular fibrillation and may appear dead with no palpable pulse or audible heartbeat. Body temperatures below 25.degree. C. (77.degree. F.) cause cardio-pulmonary arrest and death. These forms of hypothermia clearly present life-threatening medical problems complicating the treatment of the victim.
It is becoming established that the safest and most efficient technique for treating the severely hypothermic victim is by active core rewarming, i.e. the delivery of heat primarily to the body core or central circulation system (and also avoiding simultaneous rapid rewarming of the skin and extremities). Only inhalation rewarming is a suitable technique for use by paramedics and other trained emergency rescue personnel at a rescue site or during transport to hospital or clinical facilities.
Warm, moist air is also very useful for relieving laryngectomy and tracheotomy patients, and to relieve asthmatic bronchial spasms.
In the normal breathing process, inhaled air becomes warmed and humidifies as it passes through the nasal, tracheal and bronchial passages. This basic body function protects the delicate membranes in the lungs, but may not be sufficiently effective in heavy or rapid breathing of very cold dry air. During exhalation, some heat and moisture is returned to the walls of the breathing passages, but most of the heat energy and moisture is lost in the exhaled gases.
At rest and at a comfortable room temperature, the energy loss is of the order of 1 Kcal per hour, and is easily compensated by normal body functions. However, at low temperatures and high altitudes, the energy loss could be 230 Kcal and 250 grams of water per hour. This is a significant portion of the energy output of the body and contributes to the harmful effects caused by the inhalation of extremely cold air. In the absence of the ingestion of food, the mere use of warm clothing may not be sufficient to retain a desirable amount of the energy. Also, since thirst response is suppressed by extreme cold, desiccation could become a problem.
There is thus a widespread need for apparatus capable of producing heated and moist air, and in most cases such need is for air heating apparatus which is self-contained and not requiring mass electric power, compact, safe and not needing a flame to heat the air, and lightweight so as to be conveniently portable. As discussed above, one important current need for such air heating apparatus is to produce heated air to be inspired by persons through a suitable device into the lungs, which is an efficient means for warming persons suffering from body core heat loss that may have reached the stage of hypothermia. Such inspiration of heated air directly into the lungs is the most effective and safe way to warm a person and to bring hospital-type treatment to the rescue situation.
(ii) Description of the Prior Art
A number of devices have been developed in the prior art for the purpose of reducing the harmful or dangerous effects caused by the inhalation of extremely cold air. Such patented devices and techniques for heating and humidifying breathing gases have been devised for many purposes. In the field of conditioning inhalent gases and vapors, for use in underwater environments, U.S. Pat. No. 3,107,669 patented Oct. 22, 1963 by G. E. Gross may be mentioned. In that patent, the portable underwater breathing apparatus included an air inlet valve and a tubular extension adjacent the air inlet valve, with an air-treating, electric heating element sealingly disposed in that tubular extension.
U.S. Pat. No. 3,898,978 patented Aug. 12, 1975 by D. L. Marcus provided a self-contained, portable breathing gas heating system to be used by a diver for prolonged submersion in a cold environment. That device included a Vortex tube used for supplementary heating of the compressed breathing gas, a heat exchanger in an insulated container, a preheated fluid through which the breathing gas circulates in tubes, and exterior tubes for heat exchange of the gas with the environment.
U.S. Pat. No. 4,014,384 patented Mar. 29, 1977 by D. L. Marcus provided a self-contained, portable breathing gas heating system to be used by a diver for submersion in a cold environment. That device included a heat exchanger in an insulated container. The heat exchanger was in contact with preheated liquid through which the breathing gas circulated in tubing connecting the breathing gas source (tank) to the breathing outlet, which was secured in the mouth of the diver.
In the field of conditioning inhalent gases in a hospital environment, mention can be made of U.S. Pat. No. 3,902,486 patented Sept. 2, 1975 by P. Guichard. That patent provided a portble nasal diffuser comprising a respiratory assembly having a nasal mask to be worn over the nose, the assembly being provided with an air inlet and an outlet. Air was carried to pass through a filter material to the respiratory assembly and to the user. The filter could be heated by a suitable energy source or by the body of the user.
U.S. Pat. No. 4,016,878 patented Apr. 12, 1977 by D. Castel, which provided a heater and humidifier for use with a breathing mask or other breathing apparatus, to avoid unpleasant and injurious effects of prolonged breathing of cold dry air, or other breathing gas mixture. The patented device required injection and combustion of hydrogen directly in the breathing gas. In addition to the heating effect, the hydrogen combined with oxygen in the breathing gas to produce moisture.
U.S. Pat. No. 4,355,636 patented Oct. 26, 1982 by Oetjen et al provided a humidifier and heater for air to be inhaled for connection to an inhalation conduit of a respirator. That respirator included a housing having a bundle of vapor-permeable fiber tubes which had evaporation fiber wall surfaces exending therethrough. A packing was arranged adjacent each end of the housing in the tubes and sealed the space in the housing around the tubes between the packing. The tubes in the interior of the housing in the space had an exterior coating of either copper or silver. Warm water was circulated into the housing in the space around the tubes and the inhalation air was directed through the tubes, or vice versa.
U.S. Pat. No. 4,635,630 patented Jan. 13, 1987 by Noir et al provided an apparatus for heat therapy by inhalation which incorporated an enclosure designed to contain water in which two electrodes were immersed, and which were connected to an alternating current source. A tube terminating in a nozzle connected the top of this enclosure to a venturi which was connected upstream to the atmosphere and downstream to an inhalation mask, so as to form an air/water vapor mixture at a controlled temperature.
U.S. Pat. No. 4,652,408 patented Mar. 24, 1987 by Montgomery provided an inhalation apparatus which included a humidifier including a chamber having an inlet and an outlet. The chamber was releasably attached to a heater unit including a heater and a heat sensor. When the chamber and the heater unit were assembled together, the heater was in thermal contact with a heat transfer surface of the chamber at or adjacent the inlet port, while the temperature sensor was in thermal contact with the heat transfer surface at or adjacent the outlet port.
In the field of inhalation rewarming, mention may be made of U.S. Pat. No. 4,019,511 patented Apr. 26, 1977 by P. N. Choporis et al which provided a portable conditioned heated air breathing device for personal breathing for persons having respiratory problems. That device included a compartmented canister with a collapsible hose storage compartment, an air conditioning compartment and a heating compartment. It also contained an ejector for ejecting an additive into the conditioned air, as well as a structural arrangement for mixing fresh air with heated air. A filter was provided for filtering the air, and a device was provided for igniting a burner from the outside of the canister. A manually-controllable valve was provided for controlling the flow of fuel to the burner.
U.S. Pat. No. 4,245,631 patented Jan. 20, 1981 by R. A. Wilkinson et al provided a frigid air respirator to enable persons with physiological deficiencies such as cardiac or respiratory ailments to be active in frigid environments without subjecting their respiratory systems to the stress created by inhaling cold ambient air. The respirator comprising a cylindrical housing affixed to a face mask, constructed so as to permit the passage of air upon inhalation by the user into the chamber formed by the housing. A heating means was situated within the housing to increase the temperature of incoming air by radiation and a transversely positioned intake valve governed the admission of air into the respiratory tract of the user and divided the chamber formed by the housing into an internal chamber, which was contiguous with the mask cavity, and into a receiving chamber, wherein a supply of previously heated air was stored prior to inhalation. An exhaust valve was encompassed into the device to allow the expulsion of air from the internal chamber and mask cavity.
U.S. Pat. No. 4,319,566 patented Mar. 16, 1982 by Hayward et al provided an apparatus which delivered warm, water-saturated air or oxygen directly to the head, neck and thoracic core as the strategic body area to minimize "afterdrop" and gradual rewarming of core temperature without stimulating return of peripheral blood with high acidity and potassium concentration. The patented apparatus included a steam heat generating apparatus.
U.S. Pat. No. 4,430,994 patented Feb. 14, 1985 by B. E. Clawson, provided a respiratory gas heating and humidifying apparatus which made use of a humidifying element. Water was made to flow, as a film, over a heat transfer element. The respiratory gas was flowed over the water film and became more humid as it proceeded. As humidity increased during the course of flow, increased temperature was required to accomplish further humidification and so the gas temperature was increased as the humidity was increased.
U.S. Pat. No. 4,491,130 patented Jan. 1, 1985 by Dragerwerk Ag provided an emergency respirator for rapid use by a person. The emergency respirator included a container having a cartridge for material which acts to bind carbon dioxide and to liberate oxygen to gases which pass therethrough. A breathing connection was connected to one end of the container which terminated at its outer end in a mouthpiece and which defined a breathing passage interconnected into the cartridge. A jacket defined a heat storage connection to the opposite end of the container which was openable to the atmosphere. Expiration gases passed through the cartridge and were heated by the binding of the carbon dioxide. This heat was stored in the heat storage. Inspiration gases were then directed through the heat storage where they were heated before passing through the cartridge to liberate oxygen so that the incoming inspiration gases were enriched with oxygen and were heated before they were delivered to the person.
U.S. Pat. No. 4,597,917 patented July 1, 1986 by K. S. Lansford provided a highly portable means for warming and humidifying therapeutic gas to be administered to a patient. The apparatus included means for passing the therapeutic gas through an area heated by a chemical reaction which requires no outside energy source. The heated area may have included water, resulting in both heating and humidifying of the therapeutic gas. The chemical heating means involved mixing two or more chemicals to produce an exothermic reaction.
U.S. Pat. No. 4,601,287 patented July 22, 1986 by G. H. Royce Jr. provided a heated survival face mask fabricated from an air-impervious material, having a single forward protrusion forming a pivoted ambient air intake and exhaust orifice, which contained a heating element to elevate the temperature of the incoming ambient air, and which was designed to direct all of the exhausted air over the heating element, thereby to increase its efficiency.
U.S. Pat. No. 4,621,633 patented Nov. 11, 1986 by D. D. Bowles et al provided a heated oxygen system for emergency core rewarming in treating victims of severe hypothermia that includes a dry oxygen source, a separate heater compartment having an inlet connected to receive oxygen from the source, first heater means for heating the oxygen in the heater compartment, a resuscitator hose and mask connected to the outlet of the heater compartment, and second heater means for maintaining a predetermined temperature of the heated oxygen delivered to the resuscitator mask. A portable equipment case was provided for housing the oxygen system including the power source and heater controls therefor and other emergency airway equipment and supplies.
U.S. Pat. No. 4,662,352 patented May 5, 1987 by E. R. Aviles provided a catalytic heater for heating air, that contains a small percentage of hydrogen. A preheat catalytic chamber was provided within a primary catalytic chamber, and the air/hydrogen mixture was first flowed through the preheat chamber and then through the primary chamber, so that the gas was first catalytically preheated as it passed through the preheat chamber and was further heated with increased thermodynamic efficiency because of the preheating as it passed through the primary chamber. The preheat chamber was provided within massive heat sink means, preferably of brass, which obtained additional heat from the primary catalytic chamber so as to cause the preheat catalytic activity to be even further effective for overall increased thermodynamic efficiency of the system. The heat sink characteristic stabilized the output temperature of the heated gas against fluctuations.
Canadian Pat. No. 1,054,480, patented May 15, 1979 by Dragerwerke, Ag provided a filter respirator for self-protection against carbon monoxide and which had a catalyst portion which operated at high temperatures and a mouthpiece casing portion which was openable to cool respirated air by the evaporation of the saliva of the user. The respirator had a casing with an air inlet and an internal passage filled with a catalyst material and a mouthpiece casing connected to the catalyst casing with a passage for a flow of air from the catalyst casing through the mouthpiece casing. The mouthpiece portion casing contained an internal heat exchanger chamber filled with a plastic material of low thermal conductivity in the form of fibres, chips, screens, granules, balls or tubes, through which the exhaled air was passed so that the saliva adhered to the material. The subsequent inhaled air was cooled by the evaporation of the saliva. An exhalation valve was connected to the passage downstream of the passage with respect to exhalation gas flow.
Accordingly, as noted above, various techniques have been developed for heating and humidifying breathing gas, but these techniques and devices were usually complex and heavy. Thermal heaters required power sources, and were not particularly efficient in their use of energy. In a dry atmospheric environment, a humidifier must also contain stored water in some form and was thus usually heavy and bulky. For convenience and reliability such apparatus should be simple, compact and require a minimum of storable, energy-producing medium and water.
Despite the many attempts as described above that have been made in the past to provide devices and appliances for heating air for personal breathing, and for inhalation rewarming, there is still a definite need for an improved portable, conditioned-air, breathing device containing a heating unit which will condition the air and which can be utilized over a long period of time.
Thus of the patents referred to above, U.S. Pat. No. 3,107,669 required a electric heater element sealed therein. U.S. Pat. Nos. 3,898,978 and 4,014,384 required a hot water heat exchanger to heat the air, with no provision for humidifying the air. U.S. Pat. No. 3,902,486 required special means to heat a filter through which the gas passed. U.S. Pat. No. 4,355,636 required a hot water heat exchanger to heat the air. U.S. Pat. No. 4,652,408 required both an electric heater and a heat sensor.
While the system of the Castel U.S. Pat. No. 4,016,878 did indeed heat the breathing air, it was much too slow in building up sufficient heat to reach a target temperature, and large temperature fluctuations occurred between inspiration and expiration. U.S. Pat. No. 4,019,511 of Choporis used a flame as the heat source and, for humidification, required manual injection of water by the user. U.S. Pat. No. 4,245,631 required flow-control valves. U.S. Pat. No. 4,430,994 requires a compressed source of breathing gas and also required electric power for heating. The portable inhalation gas heating apparatus of the Hayward et al U.S. Pat. No. 4,319,506 required an external gas source or electric power to warm the inhalation gases. U.S. Pat. No. 4,491,130 used a porous material for heat conservation but did not teach humidification of the inhalate. U.S. Pat. No. 4,597,917 required a compressed gas source for the inhalate, didn't use a porous heat exchange material, and for humidification had the disadvantage of requiring the heating of a relatively large amount of water. U.S. Pat. No. 4,601,287 required the use of a special heating element. U.S. Pat. No. 4,621,633 required the use of a separate heater compartment. U.S. Pat. No. 4,662,352 required the use of a preheat catalytic chamber as well as a heat-sink primary catalytic chamber.
Canadian Pat. No. 1,054,480 used a porous heat exchange material for cooling purposes.